Intraguild predation on the aphid parasitoid Lysiphlebus fabarum (Marshall) (Hymenoptera:Aphidiidae):: mortality risks and behavioral decisions made under the threats of predation

Intraguild predation (IGP) is a primordial mortality factor that generates consequences for the coexistence of species in natural communities as well as for the implementation of antagonists in biological control programs. Among parasitoids and predators the most frequent form of IGP is asymmetric. Because it exerts a strong selection pressure on the inferior parasitoids it seems to be likely that these antagonists have evolved strategies to minimize IGP. Our study traced the behavior of the aphid parasitoid Lysiphlebus fabarum (Marshall) which is able to exploit the enemy free space in ant protected aphid colonies. In the agricultural landscape, L. fabarum frequently forages in aphid colonies without ant protection where it is exposed to situations with an extraordinary high risk of predation by aphidophagous predators. In the current study, we investigated predation risks for different developmental stages of L. fabarum and behavioral decisions made under the risk of predation by foraging females. All developmental stages of L. fabarum suffered from a high risk of predation in confrontations with most of the tested aphidophagous predators. Only aphid mummies turned out to be a less frequent IG-prey compared to unparasitized aphids when found simultaneously with adult Coccinella septempunctata L. and larvae of Episyrphus balteatus de Geer. Nevertheless, foraging females of L. fabarum did not avoid the presence of predators nor displayed an effective defense behavior in direct confrontations with any of the tested predator species. Coccinellids, syrphids as well as chrysopids proved capable of killing an adult parasitoid. The discrepancies between the observed predation risks and the lack of behavioral adaptations of adult L. fabarum are discussed in different contexts. (C) 2002 Elsevier Science (USA). All rights reserved.